During the early years of the Galactic Civil War, the Rebellion learned that the best strategy for weakening the Empire lied in disrupting the Empire's commerce. Rebel starfighters would hyper into the vicinity of an Imperial convoy, make a quick assault and then hyper back home again. This would later be dubbed as "Hit-and-Fade" strikes.

These strikes proved very effective in damaging or completely destroying the inadiquately defended Imperial convoys. And yet the Empire wouldn't devote one of their large Star Destroyers to protect each convoy because they were simply not designed for escort duty. Therefor, Kuat Drive Yards was commissioned to design an escort vessel for the specific job of protecting convoys.

Kuat Drive Yards eventually decided to use a design similiar to the Nebulon-A class Torpedo Frigate. This new design, the Nebulon-B, proved to be an excellent escort starship. The hull and shielding were strong and weapons were placed on strategic areas of the hull giving excellent laser cannon coverage. The Nebulon-B could also carry two squadrons of TIE Fighters and several transports and freighters could be docked in the hangerbay and/or external docking ports. Sophisticated sensors and deep-space, multifrequency antenna allowed them to function as long-range scouts or to relay battle information to a command vessel. And the firepower of the Nebulon-B overpowered most other medium starships making it formidble against both starfighters and larger vessels.

The Nebulon-B soon scored many kills against Rebel starfighters attacking Imperial convoys. However, the Rebellion, taking advantage of inexpierienced Imperial starship commanders, were in quite a few cases able to trap a Nebulon-B and capture it. There are also a few instances where the crews of these frigates would defect bringing their vessel with them.

The Nebulon-B was the Rebellion's first capital starship to enter into their small fleet. When the Mon Calimari Cruisers and other large vessels were added, Escort Frigates were assigned duties such as medical frigates, command ships, long-range reconnaissance ships, and search and rescue frigates.

The Rebels weren't the only ones to aquire these frigates. Many nuetral and pirate factions used these as their flagships or large capital starships since they couldn't aquire larger cruisers as easily.